Variable angle internal reflection attachment



United States Patent Inventor Paul A. Wilks, Jr.

Darien, Connecticut Appl. No. 681,472

Filed Nov. 8, I967 Patented Nov. 24,1970

Assignee Wilks Scientific Corporation South Norwalk, Connecticut acorporation of Connecticut VARIABLE ANGLE INTERNAL REFLECTION ATTACHMENT2 Claims, 10 Drawing Figs.

[56] References Cited UNITED STATES PATENTS 3,157,788 11/1964 Roche356/244 3,332,315 7/1967 Wilks,.lr 356/244 3,240,111 3/1966 Sherman etall.

Primary Examiner- Ronald L. Wibert Assistant Examiner-V. P. McGrawAtt0rney-Smythe & Moore US. Cl.. 356/244 Int. Cl ..G01n 21/16; GOlj 3/00Field ofSearch 356/244, 74; ATR/Digest 1. VARIABLE ANGLE INTERNALREFLECTION ATTACHMENT SPECIFICATION The present invention relates tointernal reflection spectroscopy and more particularly to an attachmentfor varying the angle of incidence of a beam of radiation entering asample wherein the beam is reflected within the sample a multhose wavelengths where the material absorbs energy. This attenuated radiation,when measured and plotted as a function of wave length by aspectrophotometer. will give an absorption spectrum characteristic ofthe material.

The depth to which the radiation penetrates is a function of: (l) Thewave length oflight, (2) The refractiveindex-of both of incidence.Thcinternal reflection means is mounted on a member which is linearlymovable on the platform by rotation of an adjusting knob. Themovablemember and the reflecting surfaces are linked in pantographlike fashionby a scissorsjack assembly. By rotating the single adjusting knob, thereflecting surfaces are moved in synchronism with the internalreflection means mounted on the movable member so that the beam of thereflector and sample, and (3) The angleof incident radiation. If thedepth of penetration versus angle of incidence is plotted in a regionwhere there is maximum absorption by the sample. the penetration willincrease most rapidly when the angle of incidence at the interfacebetween the sample and prism is very near thecritical angle but it isrelativelyslight at angles well removed from the critical angle.

Nearly all the energy goes into the sample when the critical angle isexceeded.

A typical'plot of the index of refraction of a material versus wavelength in the vicinity of an absorption band willshow that the index ofrefraction undergoes radical variation in this region. There will be apoint at which the index of the sample is greater than that of thereflector. At this'wave length, there is no angle of incidence at whichinternal reflection can take place and nearly allthe energy will passinto the sample. The recorded internal reflection absorption band will,thus, be very strong but broadened toward long wave length and, hence,greatly distorted as compared to that measured by transmission.

It will be apparent that in order to obtain internal reflection spectrathat are nearly identical to transmissionspectra a rela radiation isheld in focus on the entrance face of the plate at each angle ofincidence.

Other objects, advantages and features of the present invention willbecome apparent upon'reference to the accompanying description anddrawings, which are merely exemplary.

In the drawings: 1

,FIG. I.is a top plan view of the variable angle internal reflectionattachment of the present invention;

FIG. 2 is a front elevational view ofthe apparatus of FIG. I;

FIG. 3 is a bottom plan view of the apparatus shown in FIG. I with theenclosure removed to illustrate the connecting linkage;

FIG. 4 is an elevational view of thc'apparatus illustrated in FIG. 3;

FIG. 5 is a top plan view ofthe apparatus of FIG. I but with thereflecting surfaces removed to illustrate the mounting means therefor;

FIG. 6 is a sectional view taken along the line 6.6 ofFlG. 3;

FIG. 7 is a sectional view taken along the line 7-7 of FIG. 3;

FIG. Sis a plan view ofa portion of the linkage illustrated in FIG. 3with the links having the reflecting surfaces mounted thereon beingshown in shaded lines and the remaining components ofthe linkagesystemshown in dash lines;

FIG. 9 is'a view similar to that of FIG. 8 but showing schematically thelinkage system and the movement of the reflecting surface; and

FIG. 10 is a schematic view illustrating how movement of the reflectingsurfaces varies the angle of incidence of a beam of radiation to theentrance of a sample for multiple internal tively high' index reflectorshould be used. Also, an overall Itis possible, however. to multiply theamount ofabsorption by multiplying the number of reflections. This isanalogous to increasing the path length in transmission cells. Themultiple reflection approach can thus produce undistorted spectra of anydesired intensity provided there are enough reflections.

One of the objects of the present invention is to provide an improvedapparatus for varying the angle of incident radiation with a multipleinternal reflector plate.

Another of the objects of the present invention is to provide anapparatus for varying the angle of incident radiation onto a multipleinternal reflection plate while holding the beam of radiation in focusat the entrance to the plate.

In one aspect ofthe invention there maybe provided a varition means. Aplurality of reflecting surfacesare movably mounted. on the platform toreflect a beam of radiation into and out of the internal reflectionmeans. Means operatively connect the internal reflection mean and theplurality of reflecting surfaces for holding a beam of radiation infocus on the entrance of the internal reflection mean at varying anglesreflection therein.

Proceeding next to the drawings IYlIdI'tilI'! like reference symbolsindicate the same parts throughout the -arious views a specificembodiment of the present invention will be described in detail.

As may be seen in FIGS. 1 and'2, the attachment according to the presentinvention is indicated generally at 10 and comprises a base 11 which isin the form of a casing or enclosure with an upper surface or platform12.

A sample platform 13 ismovably mounted between fixed guides 14 and 15secured to top face 12 with guide 14 having an index lothereon whichregisters with ascale of angles 17 on the sample platform. The angles ofthe scale 17 represent angles of incidence of a beam of radiation to asample carried in a fixed plate sample holder (not shown in thedrawings) but which ismounted on the movable sample platform 13.

Also'mounted on the top face 12 are reflecting surfaces I8,

19, 20 and 2I. Each of the reflecting surfaces are secured in adjustingknob 23 on the top thereof to adjust by rotation the reflectingsurfaces.

Referring next to FIGS. 3 and 4, the adjusting mechanism for moving thereflecting surfaces in conjunction with the sample platform comprises ablock 24 mounted on the underside of the sample platform and having, athreaded bore therethrough. A threaded shaft 25 is journaled at 26 and27 within space 11 andis threadedly engaged with the threaded bore ofblock 24. The outer end of the shaft indicated at 28 maybe provided withan adjusting knob29 illustrated in FIGS.

. land 2.

' able angle multiple internal reflection apparatushaving a platformupon which there is movably mounted an internal reflec- The linkagesystem actually comprises two mirror opposite pantograph linkagearrangements which may be seen'in FIG. 3. The linkage comprises afirstlink 30 which has one end pivotally mounted at 31 and a slot 32 in itsother end. Pivot mount 31 is'a pin which projects above the top surface12 and the reflectingsurfaces 18 and 21 are mounted thereon.

A second link 33 is provided which has a slot 34 in its inner end and apivot pin 35 at its other end.

A connecting'link 36 is connected between the pivot point 31 and pivotpin 35. y

Pin 35 of second link 33 extends upwardly beyond the top surface througharcuate slot 37 and reflecting surfaces 19 and 20 are attached to thesepins.

Links 38 and 39 are pivotally connected at 40 to the movable sampleplatform and link 38. is pivotally connected to pin 35. Link 39 isconnected to pin 41 which is guided in slot 34 of link 33. There is-alink 42 connected between pin 41 and a pin 43 mounted on connectinglinks 36.

A link 44 is pivotally connected between pin 43 and a pin 45 which isguided in slot 32. There is a remaining link 46 pivotally connectedbetween afixed pivot pin 47 and the pin 45.

As can be seen in H6. 6, movable sample platform 13 may be provided withvertical pins 48 upon which the sample holder is mounted. The platformis guided on the undersurface of the top surface 12 by antifrictionballbearings 49. Links 38 and 39 are separated by an antifrictionsurface 50 which may be ofa plastic such as teflon or the like. Afurther bearing 51 is provided surrounding pin 40 and mounted on theunderside of the movable sample platform 13. A somewhat similararrangement of antifriction bearings maybe used for the remainingpivotal and slot connections of the linkage assembly. Another suchpivotal connection may be seen in FIG. 7. it can be seen that the link33 is secured to the pin 35 by means of set screw 52.

'The movement of the various links which results in repositioning of thereflecting surfaces may be seen in FIGS. 8 and 9.

In FIG. 10, a beam of radiation is'indicated at 53 and is reflected fromreflecting surface 18 onto reflecting surface 19 and then to entranceface 54 of a' sample 55 held between reflecting surfaces 56 and 57. 'Thebeam is multireflected within the sample as indicated schematically.

Movement of the reflecting surfaces 18 and 19 and of the sample platform13 to vary the angle .of incidence will cause the beam of radiation tofollow the path of the dash lines indicated at 58. It will be seen thatthe angle of incidence of beam 58 with entrance face 54 of the samplewill be varied from that of beam 53.

It will be apparent that during the synchronousmovement of thereflecting surfaces and the sample platform, the distances betweenreflecting surfaces 18 and 19 and 21 and 20 will remain constant.Accordingly, the image of the radiation beam will be constantly focusedon the entrance face of the sample. Further requirements of the opticalsystem compris ing the reflecting surfaces and the sample are that thepcrpen dicular to reflecting surface 18 must bisect the angle betweenreflected from said first re the incoming beam and the reflecting beamgoing to reflecting surface 19. The perpendicular to reflecting surface20 must bisect the angle from exit face of the sample to reflectingsurface 20 and to reflecting surface 21. The perpendicular to reflectingsurface 21 must bisect the angle formed by reflecting surfaces 21, 20and the entrance slit of the spectrometer. The spectrometer may bepositioned behind a plate 59 mounted on base 11 as shown in FIG. 1.

Thus it can be seen that the present invention provides an attachmentfor, making multiple intern-a1 reflection measurements at a continuouslyvarying angle of incidence. The reflecting surfaces are interconnectedby a linkage arrangement which. together with the sample platform, ismoved to maintain the proper relationship between the reflectingsurfaces and the sample platform.

It is to be understood that various details of construction andarrangement of parts may be'made'without departing from the spirit ofthe invention except as defined in the ap pended claims.

.lclaim:

' 1. ln a variable' angle multiple internal reflection apparatus. thecombination including a platform. a movable multiple internal reflectionplate holding means, a first reflecting surface means adjustably mountedon said platform for receiving a beam of radiation. a second reflectingsurface means-adjustably mounted on said latform for receivin the beamecting surface and redlecting the beam to the entrance face of amultiple internal reflection plate means on said holding means, a thirdreflecting surface means adjustably mounted on said platform forreceiving said beam from the exit face of said multiple internalreflection plate. a fourth reflecting surface means adjustably mountedon said platform for receiving the beam reflected from said thirdreflecting surface means and reflecting the beam outwardly of saidapparatus, and linkage means connecting said mi ltiple reflection plateholding means and said four reflecting surface means, said linkage meansbeing arranged to hold the distance constant between said first andsecond reflecting means and the distance constant between said third andfourth reflecting means and to hold said beam in focus relative to theentrance and exit faces of said multiple'internai plate means as theangle of incidence is changed by moving said mot able internalreflection plate meansand the angular relation of said reflect ing meansto said internal reflection plate means.

2. An apparatus as claimed in claim 1 wherein the second and thirdreflecting surface means are mounted on pivot means which are alsoarcuatcly movable.

